This invention relates to elevator hoist units and more particularly to improvements in hoist units for moving an elevator car.
In a typical elevator system a hoist unit is disposed in a machine chamber of an elevator system. The rotation of the hoist motor is transmitted to a drive sheave after the rotating speed is decreased to a suitable speed by means of a speed reduction gear having parallel shaft spur gears to move the elevator car and a counter weight up and down as disclosed in Japanese Utility Model Laid-Open No. 56-107782.
FIGS. 1 to 3 illustrate one example of a conventional elevator hoist unit of the type described above. As is well known, a conventional elevator hoist unit comprises an electric hoist motor 10 mounted on a machine bed 12 disposed on the floor 14 of a machinery chamber 16 which may be a penthouse of a building. The rotary output shaft 18 of the motor 10 has mounted thereon a coding disc 20 and a brake drum 22. Around the brake drum 22 are a pair of brake shoes 24 of an electromagnetic brake 26 mounted on the machine bed 12. The electromagnetic brake 26 comprises an electromagnetic 28 and springs 30 which are used to actuate the brake shoes 24. The rotary output shaft 18 of the motor 10 is connected at its end portion to an input shaft of a speed reduction gear unit 32 also mounted on the machine bed 12, and an output shaft 34 of the reduction gear unit 32 has mounted thereon a drive sheave 36 around which a main rope 38 is wound. One end of the rope 38 is fastened to an elevator car 40 and the other end of the rope 38 is wound around a guide sheave 42 and fastened to a counter weight 44. At its end opposite from the reduction gear unit 32, the rotary shaft 18 of the hoist motor 10 is provided with an engaging surface 46, such as a notch or notches formed in the end face of the shaft 18. This engaging surface 46 receives therein or engages with a complementary-shaped engaging end portion of a manually-operable handle so that the shaft 18 may be manually rotated during maintenance or during a power failure. As shown in FIG. 3, the speed reduction gear unit 32 comprises a pinion gear 48, which is secured on an input shaft 50 rotatably supported by bearings 52 disposed in a gear casing 54, and a spur gear 56 which is mounted on the output shaft 34 rotatably supported by bearings 58.
As is well known, as the drive sheave 36 is driven by the hoist motor 10, the elevator car 40 travels up or down the hoistway. When the car 40 is to be stopped at a floor of the building, the hoist motor 10 and the electromagnetic brake 26 are de-energized so that the brake shoes 24 are pressed against the brake drum 22 by the springs 30. When the motor 10 is energized, the electromagnetic 28 of the brake 26 is also energized, so that the brake shoes 24 are separated from the brake drum 22 against the action of the springs 30 due to the action of the energized electromagnetic 28.
The above-described conventional elevator hoist unit has several disadvantages.
The braking capacity is mainly determined by the net torque on and an inertial moment of the braking shaft. Therefore, when the unbalanced torque and the hoisting load on the output shaft 34 of the reduction gear unit 32 are large and the reduction gear ratio is small, a large braking effort is required and a large-sized brake 26, which includes large components such as the brake shoes 24, the electromagnetic 28, the springs 30, and brake levers, is necessary. This increases the cost of the brake unit 26. Sometimes, a hoist motor assembly including a bulky electromagnetic brake 26 cannot be installed within a small machine chamber 16.
Since the torque on the input shaft 18 is smaller than that of the output shaft 34 by an amount corresponding to the amount of speed reduction, it is sometimes difficult for maintenance and inspection personnel to manually operate with a handle the input shaft 18 of a machine of a low speed reduction ratio due to the torque on the input shaft 18 being too large.
Since the accuracy of speed detection depends on the number of rotations per unit time of the coding disc 20, motor speed control is difficult in a machine with a low rpm input shaft 18.